The present invention relates to an improved process for preparing 2xe2x80x2-fluoro-5-methyl-xcex2-L-arabinofuranosyluridine (generic name: Levovir, hereinafter referred to as xe2x80x9cL-FMAUxe2x80x9d) represented by formula (1), which shows anti-viral activity, especially potent anti-viral activity against hepatitis B-virus (HBV) and Epstein-Barr virus (EBV). 
International Publication No. WO 95/20595, and U.S. Pat. Nos. 5,587,362; 5,567,688; and 5,565,438 disclose L-FMAU and derivatives of formula (2): 
in which Rxe2x80x2 represents purine or pyrimidine base; and
Rxe2x80x3 represents hydrogen, acyl, alkyl, monophosphate, diphosphate or triphosphate.
Nucleoside compounds of formula (2) exhibit anti-viral activity against HBV and EBV. Among these nucleoside compounds, L-FMAU shows particularly potent anti-viral activity against HBV and EBV with very low cytotoxicity and is, therefore, preferred as an anti-viral agent. Nucleoside compounds of formula (2), including L-FMAU, are useful in the prevention and treatment of HBV infections and related conditions, such as anti-HBV antibody positive and HBV-positive conditions, chronic liver inflammation caused by HBV, cirrhosis, acute hepatitis, fulminant hepatitis, chronic persistent hepatitis, and fatigue. In addition, they can also be used for the treatment of EBV-associated disorders.
According to the method disclosed in International Publication No. WO 95/20595, L-FMAU of formula (1) may be prepared using L-xylose of formula (3) as a starting material: 
L-xylose of formula (3) cannot be obtained from natural substances and must therefore be produced by synthetic methods. When L-xylose is used as the starting material, the production cost of L-FMAU is therefore very high.
It has now been discovered that L-FMAU can be economically prepared from L-arabinose, which is present in many natural substances and, thus, is an inexpensive starting material, thereby completing the present invention.
An improved process for preparing L-FMAU is provided which uses L-arabinose as the starting material.